Since their conception over 20 years ago, three-dimensional (3D) photonic crystals have been touted for their extraordinary potential in the area of optoelectronics. However, these ideas have yet to come to fruition and the optoelectronics research space has been dominated by work on two-dimensional photonic crystals. The fundamental limiting factor for moving into 3D devices is the difficulty of fabricating 3D photonic crystals with complete or nearly complete photonic band gaps and the required electronic properties (e.g., high mobility and low defect density). A photonic band gap is analogous to an electronic band gap in that photons of a particular range of energies (frequencies) are forbidden to propagate within the crystal. This may be accomplished by modulating the dielectric constant in three dimensions in a periodic fashion. Most fabrication techniques, in particular those which are rapid, flexible in terms of structure, and commercially relevant, result in amorphous or polycrystalline materials with poor electronic properties. Those which can create single-crystal structures, such as wafer bonding and layer-by-layer assembly, are hindered by slow fabrication times and limitations on the possible photonic crystal structures. In addition, electrically driven emission has not been demonstrated for single-crystal structures resulting from fabrication techniques. Owing to this limitation, to date, 3D photonic crystals have primarily been explored for use as passive devices, such as a frequency selective reflector for a wide frequency range, since photons of the energy within the gap may be reflected from the structure.
The application space for photonic materials may be opened up if an approach for fabricating structures having electronic functionality as well as the required complex 3D structure on the proper length scales can be developed. The emergence of such 3D structures may also prove advantageous for current and future electronic devices, as well as other applications.